In a typical cellular radio system, “wireless” user equipment units (UEs) and one or more “core” networks (like the public telephone network or Internet) communicate via a radio access network (RAN). The UEs very often are mobile, e.g., cellular telephones and laptops with mobile radio communication capabilities (mobile terminals). UEs and the core networks communicate both voice and data information via the radio access network.
The radio access network services a geographical area which is divided into cell areas, with each cell area being served by a base station (BS). Thus, a base station can serve one or multiple cells. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. Base stations communicate over a radio or “air” interface with the user equipment units. In the radio access network, one or more base stations are typically connected (e.g., by landlines or microwave links) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of its base stations. In turn, the radio network controllers are typically coupled together and coupled to one or more core network service nodes which interface with one or more core networks.
One example of a radio access network is the Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN). The UTRAN is a third generation system which in some respects builds upon the radio access technology known as Global System for Mobile communications (GSM) developed in Europe. UTRAN is a wideband code division multiple access (W-CDMA) system.
In W-CDMA technology, a common frequency band allows simultaneous communication between a user equipment unit and plural base stations. Signals occupying the common frequency band are discriminated at the receiving station through spread spectrum CDMA waveform properties based on the use of a high speed, pseudo-noise (PN) code. These high speed PN codes are used to modulate signals transmitted from the base stations and the user equipment units. Transmitter stations using different PN codes (or a PN code offset in time) produce signals that can be separately demodulated at a receiving station. The high speed PN modulation also allows the receiving station to advantageously generate a received signal from a single transmitting station by combining several distinct propagation paths of the transmitted signal. In CDMA, therefore, a user equipment unit need not switch frequency when handoff of a connection is made from one cell to another. As a result, a destination cell can support a connection to a user equipment unit at the same time the origination cell continues to service the connection. Since the user equipment is always communicating through at least one cell during handover, there is no disruption to the call. Hence, the term “soft handover.” In contrast to hard handover, soft handover is a “make-before-break” switching operation.
The UTRAN accommodates both circuit-switched and packet-switched connections. Circuit-switched connections involve a radio network controller communicating with a mobile switching center (MSC) node which in turn is connected to a connection-oriented, external core network like the Public Switched Telephone Network (PSTN) and/or the Integrated Services Digital Network (ISDN). Packet-switched connections involve the radio network controller communicating with a Serving GPRS Support Node (SGSN), which in turn is connected through a backbone network and a Gateway GPRS support node (GGSN) to packet-switched core networks like the Internet and X.25 external networks. There are several interfaces of interest in the UTRAN. The interface between the radio network controllers and the core network(s) is termed the “Iu” interface. The interface between two radio network controllers is termed the “Iur” interface. The interface between a radio network controller and its base stations is termed the “Iub” interface. The interface between the user equipment unit and the base stations is known as the “air interface” or the “radio interface.”
A goal of the Third Generation Partnership Project (3GPP) is to evolve further the UTRAN and GSM-based radio access network technologies. Of particular interest here is the support of variable transmission rate services in the third generation mobile radio communications system for both real time and non-real time services. Of course, since all users share the same radio resources, the radio access network must carefully allocate resources to individual UE connections based on quality of service requirements, such as variable rate services, and on the availability of radio resources. When a core network desires to communicate with a UE, it requests services over the Iu interface from the radio access network in the form of radio access bearers (RABs) with a particular quality of service (QoS). Quality of service includes such things as data rates, speed, variability of data rate, amount and variability of delay, guaranteed versus best effort delivery, error rate, etc. A radio access bearer is a logical channel or connection through the UTRAN and over the radio interface corresponding to a single data stream. For example, one bearer carries a speech connection, another bearer carries a video connection, and a third bearer carries a packet data connection. Connections are mapped by the UTRAN onto physical transport channels. By providing radio access bearer services to the core network, the UTRAN isolates the core network from the details of radio resource handling, radio channel allocations, and radio control, e.g., soft handover.
For simplicity, the term “connection” is used hereafter.
Between the UE and the UTRAN, a connection may be mapped to one or more dedicated transport channels (DCHs) or to a common transport channel such as the random access common channel (RACH), the forward access common channel (FACH), the common packet channel (CPCH), and the downlink shared channel (DSCH). Real time connections are mapped to dedicated channels. On a dedicated channel, resources may be guaranteed to provide a particular service, such as a minimum transmission rate.
Over the Iu interface, a rate control command to the core network user of the connection can be used to at the allowed transmission rate down to a minimum guaranteed rate. Based on this minimum guaranteed rate an the core network rate control mechanism, when the UTRAN performs admission control for a newly-requested connections, it only needs to reserve radio bandwidth and other resources for the minimum guaranteed transmission rate. However, if additional radio resources are or become available, the transmission rate of that connection can be increased from the minimum guaranteed rate.
In contrast to real time connections, non-real time connections may be mapped either to dedicated channels or common channels. Typically, non-real time connections are mapped to dedicated channels when a large volume of data is to be transmit ed. Conversely, non-real time connections are typically mapped to common channels when the data activity level is lower. Since the UTRAN has no guarantees regarding a minimum rate that it must fulfill, the UTRAN may adapt the transmission rate of non-real time connections continuously to the available radio bandwidth without having to signal such a change back to the core network user over the Iu interface.
If during the lifetime of the connection, the UE moves to a cell controlled by another RNC, (referred to as a drift RNC (DRNC)), then the RNC that was initially set up to handle the connection for the UE, (referred to as the serving RNC(SRNC)), must request radio resources for the connection from the drift RNC over the Iur interface. If that request is granted, a transmission path is established for the connection between the SRNC and the DRNC to the UE through a base station controlled by the DRNC.
If the connection is mapped to a common transport channel, the drift RNC allocates the UE connection to a specific common transport channel, e.g., the FACH. Accordingly, information for the UE is transmitted on the established connection over the Iur interface from the serving RNC to the drift RNC. The drift RNC then schedules transmission on the common channel to the UE, taking to account the amount of data to be transmitted on this common channel to other UEs as well. For example, the drift RNC may use a “credit-based” data packet flow control protocol over the Iur interface to limit the amount of data that needs to be buffered in the drift RNC. Thus, the drift RNC, which performs admission control in the cell in which the UE is currently located, also controls the data transmission rate or throughput in that cell. However, the drift RNC does not give the serving RNC any guarantees on the transmission rate/throughput for a connection mapped to a common transport channel.
The situation is different for a dedicated transport channel. When establishing a radio link in a cell controlled by the drift RNC, the drift RNC reserves resources for the dedicated transport channel for this UE. But data transmission on the dedicated transport channel is scheduled by the serving RNC. For real time connections, the serving RNC typically forwards data to the drift RNC at the same transmission rate the data is received from the core network. For non-real time connections, the serving RNC typically transmits the data received from the core network user at the maximum possible transmission rate of the dedicated transport channel until the serving RNC transmission buffers are empty. After a time out period, the dedicated channel is released. Accordingly, the drift RNC must reserve radio resources for the maximum dedicated channel rate when performing admission control for the connection. The maximum channel rate must be reserved even if the average transmission rate over the dedicated channel will ultimately be much lower than that maximum rate.
As a result, there are inefficiencies in allocating dedicated channel resources over the Iur interface. Because the drift RNC must reserve resources for the maximum possible rate of the dedicated channel, some of the reserved radio bandwidth is not used because the serving RNC is not transmitting at the maximum rate. Precious bandwidth is wasted. It is a primary object of the present invention to avoid this inefficiency and thereby increase the capacity of the radio access network.
One possible approach to solving this problem would be for the serving RNC to provide the drift RNC with an average bit rate parameter or requirement. Unfortunately, it is difficult to define average bit rate. Moreover, for the average bit rate parameter to be useful for admission control/resource allocation in the drift RNC, the average bit rate must be determined using an accurate statistical model for the traffic distribution. Such a model is complicated and difficult to provide. A less complicated approach is needed.
A better solution is to have the drift RNC play a part in controlling the connection transmission rate by introducing a feedback type of control signal from the drift RNC through the serving RNC. Assume a connection has been established between an external network to a UE via a first RAN node and second RAN node. The transmission rate from the first RAN node to the second RAN node is regulated based on a rate control request from the second RAN node. In one example embodiment, the first and second RAN nodes correspond to a serving radio network controller and a drift radio network controller, respectively. In another example embodiment, the first and second RAN nodes correspond to a radio network controller and radio base station, respectively.
The rate control request is made based upon a congestion or load condition being monitored by the second RAN node. When the load condition is detected, the second RAN node requests the first RAN node to lower the transmission rate of information. Conversely, when the load condition is relieved, the second RAN node can request that the first RAN node increase the maximum allowed transmission rate of information. The rate control can be applied in the uplink and/or downlink directions.
In one non-limiting, example embodiment where the first and second RAN nodes are the serving and drift RNCs, a connection requested with the UE is established initially by way of a serving RNC through a serving RNC base station to the UE. When the UE moves into a cell area served by another drift RNC, the connection is maintained by way of that drift RNC and a corresponding drift RNC base station. The drift RNC monitors a condition in that cell and based on that condition, (e.g., congested, overloaded, etc.), the drift RNC requests that the serving RNC change the bit rate that the serving RNC is allowed to use, (e.g., decrease the bit rate). Accordingly, the serving RNC changes the bit rate for the connection in response to that request. Subsequently, if the drift RNC detects a change condition in the cell, (e.g., no longer congested), the drift RNC can request the serving RNC to increase the maximum allowed bit rate.
In another non-limiting example embodiment where the first and second RAN nodes are an RNC and a base station, the base station monitors a condition in that cell, and based on that condition, (e.g., congested, overloaded, etc.), the base station requests that the RNC change the bit rate that the RNC is allowed to use, (e.g., decrease the bit rate). Accordingly, the RNC changes the bit rate for the connection in response to that request. Subsequently, if the base station detects a change condition in the cell, (e.g., no longer congested), the base station can request the RNC to increase the maximum allowed bit rate.
Oftentimes, when a connection is initially established, a guaranteed minimum bit rate is specified for the connection. Accordingly, the DRNC and/or base station must ensure that there are sufficient resources to provide that guaranteed bit rate. Moreover, the drift RNC and/or base station cannot in that case request that a bit rate be used that is lower than the guaranteed bit rate.
In a UTRAN specific, example embodiment, the serving RNC sends a set of transport formats to be supported by the drift RNC for the connection. The set of transport formats includes a minimum bit rate and multiple higher bit rates that may be employed if sufficient bandwidth capacity is available. One way of lowering the bit rate is for the drift RNC request to the serving RNC to limit or employ a subset of the allowed transport formats that can be used by the serving RNC to transmit data over the transport channel.